Preheat grill to high heat.
Bring your steak to room temperature for more even cooking by letting it rest out of the fridge for ten minutes. Season generously with salt and pepper.
Meanwhile place onion in a small bowl: cover with cold water and set aside. Repeat with radishes. Remove from water when ready to use.
Place pan over medium high heat and add 2 Tbsp butter and allow it to melt.
Add the shallot and thyme and let them soften, about 2 minutes.
Add the brandy and flambe it to remove the alcohol.
Add the beef stock and green peppercorns and allow it to reduce by half.
Stir in cream and butter, and then remove from heat. Finish with 1 Tbsp of lemon juice.
Cook steak on the grill for about 4 minutes a side until medium rare and lightly charred.
Allow steak to rest for 10 minutes before carving.
Cut ciabatta in half leaving one side intact and drizzle with olive oil. Let warm on grill until slightly crispy.
To assemble place bread cut side up and drizzle with peppercorn sauce. Top with arugula and onions. Thinly slice the steak and arrange over the arugula. Drizzle with more sauce and garnish with radishes.